1. Field of the Invention
The present invention relates to a thin-film electroluminescence (EL) device capable of displaying multiple colors using color filters.
2. Description of the Prior Art
Generally, thin-film EL devices have a laminated structure wherein a plurality of thin layers or films are superimposed on one another.
FIG. 1 shows a conventional thin-film EL device having such a laminated structure and designed to display multiple colors. This EL device has a glass substrate 71, upper and lower electrodes, i.e., transparent electrodes and back electrodes 76 and 72, a luminescent layer 74, and upper and lower dielectric layer 75 and 73. The lower electrodes 72 are formed of Al in stripes on the glass substrate 71. The lower dielectric layer 73, the luminescent layer 74 and the upper dielectric layer 75 are sequentially formed over the lower electrodes in this order. The upper electrodes 76 made of ITO (indium tin oxide) in stripes are disposed on the upper dielectric layer 76 in such a manner as to intersect the lower electrodes 72 at right angles. Areas of the EL device where the lower and upper electrodes 72 and 76 are intersecting each other, in other words, where the lower and upper electrodes are opposed to each other, are used as picture elements. On the upper electrodes 76 are formed red and green filters alternately.
When Al electrodes are used as in the above conventional thin-film EL device, light coming from the outside tends to be reflected by the Al electrodes. This is main factor of light reflection in thin-film EL devices having Al electrodes. In addition to this factor, the laminated structure also causes light reflection to occur in the interface between the layers even though each layer is transparent. In other words, thin-film EL devices having a laminated structure tend to have a high reflectance. This is of course true with the conventional thin-film EL device of FIG. 1 and what is worse, incident light from the outside tends to be reflected not only in the picture-element areas but also in non-picture-element areas between the picture elements. Light reflection caused by the above factors eventually causes a white display and the display quality is lowered.
In order to avoid reflection of light coming from the outside, another prior art thin-film EL device has a black filter in the non-picture-element areas. A black filter can absorb external light well, so that reflected light can be greatly reduced. In this case, however, a comparatively time-consuming step of forming the black filter is required. As a result, production costs increase.